1. Field of the Invention
The present invention relates to semiconductor integrated circuits and, in particular, to a no cost technique for adding Zener zap diode aluminum bridged anti-fuse trim to a Tungsten plug process for fabricating integrated circuit structures.
2. Discussion of the Related Art
Zener zap diode anti-fuses, which depend upon bias direction to create the anti-fuse mechanism, are typically applied to processes with an interconnect of aluminum, aluminum alloy only, or an aluminum alloy with a barrier metal. An overview of Zener zap diode anti-fuse trim is presented by D. T. Comer, xe2x80x9cZener Zap Anti-Fuse Trim in VLSI Circuits,xe2x80x9d VLSI Design, 1996, Vol. 5, No. 1, pp. 89-100.
However, when Tungsten interconnect processes are used, the aluminum melt and flow mechanism that Zener zap diodes rely upon is blocked. The blocking feature is the Tungsten plug itself.
Thus, there is a need for a Zener zap anti-fuse mechanism that is utilizable in a Tungsten plug process.
The present invention provides a two-terminal Zener zap diode device that relies upon the formation of an anti-fuse through the silicon substrate. This is accomplished by the melting and flowing of an aluminum alloy through the diode to create a permanent conduction path. The use of an oversized contact permits the Tungsten plug to be eliminated from the diode structure and, thus, permits restoration of the aluminum/aluminum alloy conduction path, allowing the aluminum/aluminum alloy melt and flow mechanism to be used with a Tungsten plug process. The elimination of the Tungsten plug from the diode structure could be accomplished with a separate mask and etch step, but that would require extra processing and added cost. The technique of the present invention requires no additional processing.
As used in this document, the term xe2x80x9coversized contactxe2x80x9d is defined as a contact where the width of the contact is greater than two times the Tungsten deposition thickness. Clearly, for proper Tungsten plugs to be formed, the dimension must be less than two times the Tungsten thickness for the plug to fill properly without a center void. When the contact width is greater than two times the Tungsten thickness, the Tungsten etchback will penetrate the seam area and, if the width is large enough, the Tungsten will be removed from the contact bottom in the same manner that it is removed from the open area on the wafer.